Electrodeless gas discharge devices employing tritium as a source of ions to prime the discharge

ABSTRACT

An electrodeless, halogen gas microwave-induced discharge device, particularly adapted for use as a power limiter stage, which has no wires connected to it. Incorporated into the discharge device is a free electron emitter comprising tritium adsorbed into a layer of material such as titanium or yttrium. The tritium yields sufficient initiatory electrons to prime the microwave gap so as to yield a short interval for radio-frequency breakdown of the gas, and to yield repeatable discharge characteristics with each incident radio-frequency pulse.

United States Patent Goldie et al.

[451 DecQS, 1972 [54] ELECTRODELESS GAS DISCHARGE DEVICES EMPLOYINGTRITIUM AS A SOURCE OF IONS TO PRIME THE DISCHARGE [72] inventors: HarryGoldie, Randallstown; Michael Goldman, Pikesville, both of Md. 1 [73]Assignee: Westinghouse Electric Corporation, a Pittsburgh, Pa. V

[22] Filed: Aug. 18, 1971 21 Appl. No.: 172,847

[52] US. Cl. ..313/54, 313/223, 315/39,

[51] Int. Cl ..-...H01p 1/14 [58] Field of Search ....3l3/54, 223;333/13; 315/39 [56] References Cited UNITED STATES PATENTS 3,534,29810/1970 Goldieetal.... ..333/l3 E MICROWAVE 3,648,100 3/1972 Goldie etal. ..3 15/39 Primary Examiner-Roy Lake Assistant Examiner-Darwin R.Hostetter Attorney-F. H. Henson et al.

[5 7] ABSTRACT An electrodeless, halogen gas microwave-induced Vdischarge device, particularly adapted for use as a power limiter stage,which has no wires connected to it. Incorporated into the'dischargedevice is a free electron emitter comprising tritium adsorbed into alayer of material such as titanium or yttrium. The tritium yieldssufficient initiatory electrons to prime the microwave gap so as toyield a short interval for radiofrequency breakdown of the gas, and toyield repeatable discharge characteristics with each incidentradiofrequency pulse.

7 Claims, 3 Drawing Figures I PATENTEnncc 51912 sum-1n 1 or 2 FIG. I.

RECEIVER LOAD ' PATENTED 5 I97? 3. 705. 3 l 9 SHEET 2 BF 2 MICROWA V5ELECTRODELESS GAS DISCHARGE DEVICES EMPLOYING TRITIUM AS A SOURCE/OFIONS TO PRIME THE DISCHARGE BACKGROUND OF THE INVENTION As is known,there are various classes of electrical devices presently in use whichdepend upon ignition of an electrical gas discharge (i.e., the formationof a gaseous plasma) for their operation. One such device is a-keepalivestage used as aradar receiver protector. Such protectors are placed in awave guide leading from a circulator to the receiverand consist of aquartz or the like capsule containing a halogen gas, preferablychlorine. Assuming that a suitable source of ions or electrons ispresent to prime the discharge within the gas, and assuming that thecapsule isdisposed in an aperture formed in a thin iris plate in thepath of wave energy passing through the wave guide, a high energy pulse(such as that which would damage the receiver) will ionize the halogengas. The resulting increase in electron density represents an increasein permittivity of the aperture in the iris plate, changing itscapacitance and detuning the circuit. This causes the high energy pulse,which might otherwise damage the receiver, to be reflected. On the otherhand, a low energy pulse, such as that reflected as an echo from adistant target, will not cause ionization of the halogen gas with theresult that the low energy pulse will pass through the iris plate to thereceiver, as is intended. I

A keepalive. stage of the type described above depends for its operationupon ignition of an'electrical gas discharge. Furthermore, the devicerequires a source of ions-or electrons to prime the discharge, the"performance of the device being beneficially affected by increasedavailability of priming or initiatory' electrons.

The development of practical radar receiver protectors using halogengases has not as yet been realized due to the fact that in the past thesource of priming electrons to the electron gap has'been a cold-cathodemetal electron discharge. The chlorine, being highly SUMMARY OF THElNVENTION In accordance with the present invention, a gaseous dischargedevice is provided which depends for its operation upon a source ofpriming radiation, and wherein the priming radiation source comprisestritium adsorbed into a layer of material such as titanium or yttrium.The tritium provides only low energy radiation (i.e., electrons) withpenetrating power sufficiently small to allow high activities ofradiation to be used safely. The gas, usually a halogen such aschlorine, is contained within a quartz or the like capsule having alayer of titanium or yttrium with adsorbed tritium on an interiorsurface thereof. The low energy radiation is introduced into the gaswithin the capsule through a thin insulating surface such as silica.With an arrangement of this type, the chemical composition and presenceof the original fill gas is not changed regardless of the frequency ornumber of pulse breakdowns of the gas.

electrons tritium adsorbed into a layer of titanium or yttrium. Thesuccessful realization of the invention, when incorporated into amultistage radar receiver protector, will yield an all-halogen tube withan extremely fast recovery period and long operating life since in nopart of the device does any gas come into contact with a metal surface.Furthermore, the invention enables an assured first pulse breakdownwhether the stage has been passive for periods of microseconds or monthsand reproducible discharge characteristics on a pulseto-pulse basis eventhough the time between successive pulses is from microseconds toseconds.

The above and other objects and features of the invention will becomeapparent from the following detailed description taken in connectionwith the accompanying drawings which form a part of this specification,and in-which:

FIG. 1 is an illustration of the electrical discharge device of theinvention as applied to a keepalive stage positioned within a wave guideleading to a radar receiver or the like;

H6. 2 is an enlarged cross-sectional view showing the manner in whichtritium is adsorbed into a layer of titanium or yttrium on an interiorsurface of the keepalive stage of FIG. 1; and

FIG. 3 illustrates a typical application of the gaseous discharge deviceof the invention.

With reference now to the drawings, and particularly to FIG. 1, there isshown a wave guide section 10 having a thin iris plate or resonantelement 12 extending across its width and perpendicular to the axis ofthe wave guide. For X-band operation, the thickness of this element maytypically be about mils. Provided in the iris plate 12 is an aperture 14provided at its top and bottom with truncated triangular portions 16 and18 separated by a gap 20. With this arrangement, the electric fieldinduced by the microwave energy flowing through the wave guide 10 willbe concentratedacross the gap 20 between the ends of the truncatedtriangular portions 16 and 18.

Provided in the iris plate 12 is a hole or bore 22 typically having adiameter of about 50 mils. The upper end of the bore 22, whichterminates at the top of the truncated triangular extension 18, receivesthe lower end of a capillary 24 extending downwardly from a capsule 26charged with a halogen gas, such as chlorine. As will be explainedhereinafter, the capsule 26 and its communicating, integral capillary 24are preferably formed from quartz. The upper end wall 28 of the capsuleis provided on its undersurface and within the interior of the capsule26 with a layer of titanium or yttrium having tritium adsorbed therein.With this arrangement, tritium will radiate beta rays (i.e., electrons)vinto the halogen gas within the capsule 26 to act as a priming source ofelectrons to facilitate rapid microwave breakdown of the gas.

When a pulse of microwave energy above a predetermined amplitude reachesthe iris plate 12, the gas within the capsule 26 will ionize, theelectron density representing an increase in permittivity between thetriangular portions 16 and 18. This changes the capacitance of theresonant element and detunes the circuit with the result that the waveenergy is reflected. On the other hand, a pulse of microwave energybelow the aforesaid predetermined amplitude will not ionize the gas andwill pass through the iris plate 12.

The details of the capsule 26 and its integral, capillary portion 24 areshown in FIG. 2. The capillary is connected to an upper cup-shapedportion 30, fitted with a cover plate comprising the end wall 28.Preferably, the capsule is formed from quartz as is the cover plate 28.Deposited on the undersurface of the cover plate 28 by vacuum-depositiontechniques is a thin film 32 of titanium or yttrium. This typically hasa thickness in the range of about 7,000 to 12,000 Angstrom units.Following deposition of the titanium or yttrium, molecular tritium isadsorbed into the film at relatively high temperatures, on the order of400C. A layer of titanium dioxide or yttrium oxide 34 is formed on theundersurface of the layer 32 by aging in an oxygen atmosphere. Finally,a layer of silicon dioxide 36, having a thickness in the range of about1,000 to 3,000 Angstrom units, is deposited over the metal-oxidesurface. The deposition is typically performed by thermal evaporation ofsilicon monoxide in the vicinity of the metal-oxide surface in a lowpressure oxygen ambient of about torr.

The silicon dioxide layer 36 is deposited to a thickness which is lessthan the range of the tritium beta radiation in silica, thereby allowingan appreciable portion of the beta radiation to enter the dischargevolume, yet preventing surface desorption and subsequent release oftritium molecules or atoms into the discharge volume. The maximum rangeof IO KEV beta radiation is 0.2 mg/cm as measured for aluminumadsorbers. This result is applicable to silica. For a range of 0.2 mg/cmin silica, a silica thickness of 8,000 Angstrom units is required tostop the beta radiation. Accordingly, the thickness of the layer 36 mustbe less than 8,000 Angstrom units.

The halogen gas within the capsule 26, preferably chlorine, is filled ata pressure of about 10 torr. In certain circumstances, the smallertruncated triangular portion 16 can be either eliminated or increased tothe same size as the other truncated portion 18, depending upon theapplication. The loaded 0 is typically 4 to 7. The ejected betas fromthe tritium cannot penetrate a surface more than a mil or two thick and,therefore, the device is safe to handle. The silicon dioxide layer 36acts to prevent any chemical reaction between the tritium host metal andthe neutral chlorine. Negligible ionization will occur in the vicinityof the beta emitter, so that sputtering of the silica layer by positiveions will not occur.

A typical use of the device of FIGS. 1 and 2 is shown in FIG. 3. A radartransmitter 38 is connected through a circulator 40 to an antenna 42.The antenna 42, in turn, is connected through the same circulator 40 toa dummy load 44 and through a multistage receiver pro tector 46 to aradar receiver 48. The multistage protector 46 includes three stages A,B and C, each of which includes a gaseous discharge device such as thatshown in FIGS. 1 and 2. The first stage A is designed to handlemegawatts, the second stage B is designed to handle tens of watts andthe third or last stage C is designed to handle milliwatts.

Pulses transmitted from the transmitter 38 will have a ma nituge ofabout I megawatt. Some of this energy may e re ected from the antenna 42before transmission and have a magnitude of about 8 to kilowatts. These,therefore, will trigger one or more of the gaseous discharge deviceswithin the protector 46 and cause the energy in the range of about 8 to80 kilowatts to be reflected to the dummy load 44. Echoes from a distanttarget received by the antenna 42, however, will have a magnitude in therange of about 10 to 10' watts. These will not ionize the gas in thekeepalive stages and, consequently, will pass through to the receiver.

Although the invention has been shown in connection with a certainspecific embodiment, it will be readily apparent to those skilled in theart that various changes in form and arrangement of parts may be made tosuit requirements without departing from the spirit and scope of theinvention.

We claim as our invention:

1. In a gaseous discharge device, a capsule, an ionizable gas withinsaid capsule, and a material selected from the group consisting oftitanium and yttrium having adsorbed therein tritium providing a sourceof primary radiation for said discharge device.

2. The gaseous discharge device of claim 1 wherein said capsule isformed from quartz.

3. The gaseous discharge device of claim 2 wherein said materialselected from the group consisting of titanium and yttrium is depositedon an interior surface of said quartz capsule, and a layer of silicondioxide covering said material selected from the group consisting oftitanium and yttrium.

4. The gaseous discharge device of claim 3 wherein said layer ofmaterial selected from the group consisting of titanium and yttrium hasa thickness in the range of about 7,000 to 12,000 Angstrom units andsaid layer of silicon dioxide has a thickness in the range of about1,000 to 3,000 Angstrom units.

5. The gaseous discharge device of claim 1 wherein said ionizable gas isa halogen.

6. The gaseous discharge device of claim 5 wherein said ionizable gascomprises chlorine.

7. The gaseous discharge device of claim 1 wherein said capsule has anupper cup-shaped portion and a lower downwardly-extending capillaryportion disposed in a gap formed by an aperture in an iris plateextending transversely across a wave guide.

2. The gaseous discharge device of claim 1 wherein said capsule isformed from quartz.
 3. The gaseous discharge device of claim 2 whereinsaid material selected from the group consisting of titanium and yttriumis deposited on an interior surface of said quartz capsule, and a layerof silicon dioxide covering said material selected from the groupconsisting of titanium and yttrium.
 4. The gaseous discharge device ofclaim 3 wherein said layer of material selected from the groupconsisting of titanium and yttrium has a thickness in the range of about7,000 to 12,000 Angstrom units and said layer of silicon dioxide has athickness in the range of about 1,000 to 3,000 Angstrom units.
 5. Thegaseous discharge device of claim 1 wherein said ionizable gas is ahalogen.
 6. The gaseous discharge device of claim 5 wherein saidionizable gas comprises chlorine.
 7. The gaseous discharge device ofclaim 1 wherein said capsule has an upper cup-shaped portion and a lowerdownwardly-extending capillary portion disposed in a gap formed by anaperture in an iris plate extending transversely across a wave guide.